With technology advancement, electronic products are designed to provide more and more functions and as a result, a single power supply is barely sufficient for some electronic products. Consequently, there is a trend for a power converter to provide multiple supply voltages. FIG. 1 is a circuit diagram of a conventional single-inductor dual-output (SIDO) power converter 10 for providing two supply voltages, which includes a switch SW1 coupled between a power input terminal 12 and an inductor L, two switches SW2 and SW3 coupled between a ground terminal GND and two terminals of the inductor L respectively, and two switches SW4 and SW5 coupled between the inductor L and two power output terminals 14 and 16 respectively.
FIG. 2 is a diagram to illustrate a control method for the power converter 10 of FIG. 1, in which waveform 18 represents an inductor current IL in the inductor L of the power converter 10. Assuming that the power output terminals 14 and 16 of the power converter 10 provide buck output and boost output respectively, the control method begins by turning on the switches SW1 and SW4 to establish a power path P1 and as a result, the power source VIN supplies power to the power output terminal 14 via the power path P1 and charges the inductor L simultaneously. The inductor current IL increases at a slope equal to (VIN−VOA)L, as show by the waveform 18, where VOA is the output voltage at the power output terminal 14. When the output voltage VOA reaches a preset value, the switch SW1 is turned off and the switch SW2 is turned on, thereby disconnecting the power input terminal VIN from the inductor L and establishing a power path P2, by which the inductor L supplies power to the power output terminal 14 to maintain a stable output current and in consequence, the inductor current IL decreases at a slope equal to −VOA/L. When the inductor current IL falls down to a preset level IDC, the switch SW4 is turned off and the switch SW3 is turned on to establish a power path P5. In this case, the unreleased energy in the inductor L will generate a freewheeling current in the inductor L. Following that, the switch SW2 is turned off and the switch SW1 is turned on to restore the connection with the power input terminal VIN and thus establish a power path P3, by which the inductor L is recharged and thereby the inductor current IL increases at a slope equal to VIN/L. When the inductor current IL increases to a preset level IBT, the switch SW3 is turned off and the switch SW5 is turned on, thus establishing a power path P4 to supply power to the power output terminal 16. Hence, the inductor current IL decreases at a slope equal to (VIN−VOB)/L, where VOB is the output voltage at the power output terminal 16. As soon as the output voltage VOB reaches a preset value, the switches SW 1 and SW5 are turned off and the switches SW2 and SW3 are turned on to establish the power path P5 to preserve the unreleased energy in the inductor L.
As shown in FIG. 1, the conventional SIDO power converter 10 requires five switches SW1-SW5 to generate two output voltages VOA and VOB, and each of the power paths P1-P5 has two switches for power delivery therethrough, resulting in greater conduction loss. In addition, each switch needs a driver to drive and the switching loss and gate drive loss resulted respectively from the switches and the drivers cannot be ignored.
Therefore, it is desired a SIMO power converter with reduced conduction loss, switching loss, and gate drive loss.